Motivation: The synapse is integral to the function of the brain and may be an important source of dysfunction underlying many neuropsychiatric disorders. Consequently, it is an excellent candidate for large-scale genomic and proteomic study. However, while the tools and databases available for the annotation of high-throughput DNA and protein are generally robust, a comprehensive resource dedicated to the integration of information about the synapse is lacking.
Results: We present an integrated database, called SynaptomeDB, to retrieve and annotate genes comprising the synaptome. These genes encode components of the synapse including neurotransmitters and their receptors, adhesion/cytoskeletal proteins, scaffold proteins, membrane transporters. SynaptomeDB integrates various and complex data sources for synaptic genes and proteins.
Supplementary data are available at Bioinformatics online.
The rate of progression of chronic kidney disease (CKD) is difficult to predict using single measurements of serum creatinine or proteinuria. On the other hand, documented tubulointerstitial disease presages worsening CKD, but kidney biopsy is not practical for routine use and generally does not sample the tubulointerstitial compartment of the medulla. Perhaps a urine test that correlates with specific histological findings may serve as a surrogate for the kidney biopsy. Here we compared both immunoblot analysis (under non-reducing conditions) and a commercially available monomer immunoassays of Neutrophil Gelatinase Associated Lipocalin (NGAL) with pathological changes found in kidney biopsies, to determine whether specific histological characteristics associated with a specific NGAL species. We found that the urine of patients with advanced CKD contained NGAL monomers as well as higher molecular weight complexes containing NGAL, identified by MALDI-TOF/TOF mass spectroscopy. The NGAL monomer significantly correlated with glomerular filtration rate, interstitial fibrosis and tubular atrophy. Hence, specific assays of the NGAL monomer implicate histology associated with progressive, severe CKD.
This study aimed to determine the diagnostic and prognostic value of urinary biomarkers of intrinsic acute kidney injury (AKI) when patients were triaged in the emergency department.
Intrinsic AKI is associated with nephron injury and results in poor clinical outcomes. Several urinary biomarkers have been proposed to detect and measure intrinsic AKI.
In a multicenter prospective cohort study, 5 urinary biomarkers (urinary neutrophil gelatinase–associated lipocalin, kidney injury molecule-1, urinary liver-type fatty acid binding protein, urinary interleukin-18, and cystatin C) were measured in 1,635 unselected emergency department patients at the time of hospital admission. We determined whether the biomarkers diagnosed intrinsic AKI and predicted adverse outcomes during hospitalization.
All biomarkers were elevated in intrinsic AKI, but urinary neutrophil gelatinase-associated lipocalin was most useful (81% specificity, 68% sensitivity at a 104-ng/ml cutoff) and predictive of the severity and duration of AKI. Intrinsic AKI was strongly associated with adverse in-hospital outcomes. Urinary neutrophil gelatinase-associated lipocalin and urinary kidney injury molecule 1 predicted a composite outcome of dialysis initiation or death during hospitalization, and both improved the net risk classification compared with conventional assessments. These biomarkers also identified a substantial subpopulation with low serum creatinine at hospital admission, but who were at risk of adverse events.
Urinary biomarkers of nephron damage enable prospective diagnostic and prognostic stratification in the emergency department.
acute kidney injury; biomarkers; outcomes
Background. Urinary tract obstruction (UTO) is a common problem that can lead to permanent loss of kidney function. Unilateral UTO may be difficult to diagnose. Urinary neutrophil gelatinase-associated Lipocalin (uNGAL) may identify unilateral and bilateral UTO.
Methods. Retrospective case–control study of patients undergoing hospital admission at three sites. UTO was determined by review of medical records and cases were matched to control patients. uNGAL was measured by immunoblot.
Results. Twenty-four unilateral UTO and 15 bilateral UTO cases were identified. Admission serum creatinine (sCr) (milligram per decilitre) was significantly higher in bilateral UTO, 2.0 (1.1–5.3), but not unilateral UTO, 1.1 (0.8–1.5), compared to controls, 0.9 (0.8–1.2). uNGAL (nanogram per millilitre) was significantly higher both in patients with bilateral UTO, 140 (40–450), and unilateral UTO, 50 (20–100), compared to controls, 20 (10–45).
Discussion. uNGAL identifies kidney injury in unilateral and bilateral UTO even in the absence of an elevated sCr.
acute kidney injury; biomarkers; neutrophil gelatinase-associated lipocalin; obstructive nephropathy; urinary tract obstruction
Background. Urinary neutrophil gelatinase-associated lipocalin (uNGAL) is expressed by kidney tubules that are acutely damaged, but few studies have investigated the association of neutrophil gelatinase-associated lipocalin (NGAL) with different forms of chronic kidney disease (CKD). HIV-associated nephropathy (HIVAN) is a progressive form of CKD characterized by collapsing focal segmental glomerulosclerosis and microcytic tubular dilatation that typically leads to end-stage renal disease (ESRD).
Methods. Previously, we reported that microcystic tubular dilatations specifically expressed NGAL RNA, implying that the detection of uNGAL protein could mark advanced HIVAN. To test this idea, we performed a comparative study of diverse proteinuric glomerulopathies in 25 patients who were HIV positive.
Results. Eighteen patients had HIVAN and seven had other glomerulopathies (four membranoproliferative glomerulonephritis, one membranous glomerulonephritis, one amyloid and one malarial GN). HIVAN and non-HIVAN patients did not differ with respect to age, ethnicity, serum creatinine, estimated GFR, proteinuria or the prevalence of hypocomplementemia (6 versus 29%, P = 0.18), but HIVAN patients were less likely to have HCV infections. HIVAN patients expressed 4-fold higher levels of uNGAL than the patients with other glomerulopathies [387 ± 338 versus 94 ± 101 μg/g urine creatinine (uCr), P = 0.02]. A cutpoint of 121.5 μg uNGAL/g uCr demonstrated 94% sensitivity and 71% specificity for the diagnosis of HIVAN, with an area under the receiver operator characteristic curve of 0.88.
Conclusion. In summary, while HIVAN disease is currently diagnosed only by kidney biopsy, uNGAL can distinguish HIVAN from other proteinuric glomerulopathies in the HIV-infected patient, likely because of its specific expression from characteristic microcysts.
biomarker; HIV-associated nephropathy; progressive chronic kidney disease; tubular injury; urinary neutrophil gelatinase-associated lipocalin
A synthetic approach to the C17-benzene ansamycins via metal catalyzed C-C coupling is described. Key bond formations include direct iridium catalyzed carbonyl crotylation from the alcohol oxidation level followed by chelation-controlled Sakurai-Seyferth dienylation to form the stereotriad, which is attached to the arene via Suzuki cross-coupling. The diene-containing carboxylic acid is prepared using rhodium catalyzed acetylene-aldehyde reductive C-C coupling mediated by gaseous hydrogen. Finally, RCM delivers the cytotrienin core.
Gaucher disease type 2 [OMIM #230800] is a rare lysosomal storage disorder with usual onset between 3 and 6 months of age leading to progressive neurodegeneration and death within the first 2 years of life. Rarely it may lack the characteristic symptom-free period and initially manifest prenatally or in the neonatal period. The early course of neonatal onset classic type 2 variants is not well known, and reports of early histological changes in the liver of type 2 Gaucher disease patients are scarce. We describe a patient who presented in the immediate postnatal period with cholestasis without hepatomegaly associated with hepatocellular giant-cell transformation on liver biopsy, thrombocytopenia, and failure to thrive. This was initially thought to represent neonatal giant-cell hepatitis and the correct diagnosis was not made until the age of 6 months. Hepatocellular giant transformation has not been described in the classic acute neuronopathic form of GD. However, it has been reported in congenital GD with nonimmune hydrops and neonatal hepatitis, an example of perinatal lethal Gaucher disease (PLGD), which sometimes is regarded as an entity separate from GD type 2. Our case illustrates that neonatal cholestasis may be part of a spectrum of manifestations which spans a continuum between the PLGD and classic type 2 GD. Giant cells are a nonspecific finding but may reflect the presence of a systemic inflammatory process that recently has been implicated in the brain stem degeneration associated with acute neuronopathic GD.
A single nucleotide polymorphism (rs7341475) in RELN has recently been shown to be associated with schizophrenia (SZ) in an Ashkenazi Jewish (AJ) case-control study specifically in women by Shifmen et al. We have replicated this association in women in another large independent AJ collection (721 cases, 259 female; 1455 controls, 834 female) and confirmed that it applies to both SZ and schizoaffective disorder. Further, we explore the effects of this polymorphism through quantitative trait loci (QTL) analysis of 9 SZ related factors providing information on sex-specific genotype-phenotype correlations.
Schizophrenia; Reelin; Association; Endophenotype; Sex-specific; Ashkenazi; Jewish
Characterizing structural variants in the human genome is of great importance, but a genome wide analysis to detect interspersed repeats has not been done. Thus, the degree to which mobile DNAs contribute to genetic diversity, heritable disease, and oncogenesis remains speculative. We perform transposon insertion profiling by microarray (TIP-chip) to map human L1(Ta) retrotransposons (LINE-1 s) genome-wide. This identified numerous novel human L1(Ta) insertional polymorphisms with highly variant allelic frequencies. We also explored TIP-chip's usefulness to identify candidate alleles associated with different phenotypes in clinical cohorts. Our data suggest that the occurrence of new insertions is twice as high as previously estimated, and that these repeats are under-recognized as sources of human genomic and phenotypic diversity. We have just begun to probe the universe of human L1(Ta) polymorphisms, and as TIP-chip is applied to other insertions such as Alu SINEs, it will expand the catalog of genomic variants even further.
Mutations in miRNA genes have been implicated in hearing loss in human families and mice. It is also possible that mutations in miRNA binding sites of inner ear targets alter gene expression levels and lead to hearing loss. To investigate these possibilities we screened predicted target genes of the miR-183 miRNA family known to be expressed in the inner ear sensory epithelium. In one Iranian family segregating autosomal recessive non-syndromic hearing loss (ARNSHL), we identified a homozygous variant in a predicted miR-96/182 binding site in the 3′UTR of the RDX (DFNB24) gene. However, in vitro functional studies showed that this site is not a functional target for miR-96/182. We extended our study to include the miR-183 genes themselves and 24 additional predicted target genes of the miRNA-183 family. Screening these miRNAs and target sequences in numerous families segregating either autosomal dominant non-syndromic deafness (ADNSHL) or ARNSHL did not identify any potential deafness-causing mutations. These results suggest that mutations disrupting gene regulation by the miR-183 family are not a common cause of human hearing loss.
radixin; ERM protein family; miRNA; ADNSHL; ARNSHL
Although more than 2,400 genes have been shown to contain variants that cause Mendelian disease, there are still several thousand such diseases yet to be molecularly defined. The ability of new whole-genome sequencing technologies to rapidly indentify most of the genetic variants in any given genome opens an exciting opportunity to identify these disease genes. Here we sequenced the whole genome of a single patient with the dominant Mendelian disease, metachondromatosis (OMIM 156250), and used partial linkage data from her small family to focus our search for the responsible variant. In the proband, we identified an 11 bp deletion in exon four of PTPN11, which alters frame, results in premature translation termination, and co-segregates with the phenotype. In a second metachondromatosis family, we confirmed our result by identifying a nonsense mutation in exon 4 of PTPN11 that also co-segregates with the phenotype. Sequencing PTPN11 exon 4 in 469 controls showed no such protein truncating variants, supporting the pathogenicity of these two mutations. This combination of a new technology and a classical genetic approach provides a powerful strategy to discover the genes responsible for unexplained Mendelian disorders.
Metachondromatosis (MC) is an autosomal dominant condition characterized by exostoses (osteochondromas), commonly of the hands and feet, and enchondromas of long bone metaphyses and iliac crests. MC exostoses may regress or even resolve over time, and short stature is not characteristic of MC. Here, we sequenced the whole genome of a single patient with MC and used partial linkage data from her small family to focus our search for the responsible variant. In the proband, we identified an 11 bp deletion in exon four of PTPN11, which results in premature translation termination and co-segregates with the phenotype. In a second metachondromatosis family, we identified a nonsense mutation in exon 4 of PTPN11 that also co-segregates with the phenotype. Germline gain-of-function missense mutations in PTPN11 cause an overlapping but distinct group of dominant disorders with involvement of the face, heart, skeleton, skin, and brain, including Noonan syndrome (OMIM 163950), Noonan-like disorder with multiple giant cell lesion syndrome (OMIM 163955), and LEOPARD syndrome (OMIM 151100). Nonsense mutations in PTPN11 have not been described in humans and the loss-of-function PTPN11 mutations we report here are the first to be described in human disease.
Iridium; Allylation; Transfer Hydrogenation; Allyl Acetate; 1,3-Diol; Catalytic; Enantioselective
Genome-wide association studies have identified hundreds of genetic variants associated with complex human diseases and traits, and have provided valuable insights into their genetic architecture. Most variants identified so far confer relatively small increments in risk, and explain only a small proportion of familial clustering, leading many to question how the remaining, ‘missing’ heritability can be explained. Here we examine potential sources of missing heritability and propose research strategies, including and extending beyond current genome-wide association approaches, to illuminate the genetics of complex diseases and enhance its potential to enable effective disease prevention or treatment.
Proline metabolism in mammals involves two other amino acids, glutamate and ornithine, and five enzymatic activities, Δ1-pyrroline-5-carboxylate (P5C) reductase (P5CR), proline oxidase, P5C dehydrogenase, P5C synthase and ornithine-δ-aminotransferase (OAT). With the exception of OAT, which catalyzes a reversible reaction, the other 4 enzymes are unidirectional, suggesting that proline metabolism is purpose-driven, tightly regulated, and compartmentalized. In addition, this tri-amino-acid system also links with three other pivotal metabolic systems, namely the TCA cycle, urea cycle, and pentose phosphate pathway. Abnormalities in proline metabolism are relevant in several diseases: six monogenic inborn errors involving metabolism and/or transport of proline and its immediate metabolites have been described. Recent advances in the Human Genome Project, in silico database mining techniques, and research in dissecting the molecular basis of proline metabolism prompted us to utilize functional genomic approaches to analyze human genes which encode proline metabolic enzymes in the context of gene structure, regulation of gene expression, mRNA variants, protein isoforms, and single nucleotide polymorphisms.
Apoptosis; FASTSNP; Functional genomics; OAT; OH-POX; OMIM; P53; Δ1-pyrroline-5-carboxylate (P5C); P5CDH; P5CR/PYCR; P5CS/PYCS; POX/PRODH; L-Proline; Promoter analysis; SNP
Kallmann syndrome combines anosmia, related to defective olfactory bulb morphogenesis, and hypogonadism due to gonadotropin-releasing hormone deficiency. Loss-of-function mutations in KAL1 and FGFR1 underlie the X chromosome-linked form and an autosomal dominant form of the disease, respectively. Mutations in these genes, however, only account for approximately 20% of all Kallmann syndrome cases. In a cohort of 192 patients we took a candidate gene strategy and identified ten and four different point mutations in the genes encoding the G protein-coupled prokineticin receptor-2 (PROKR2) and one of its ligands, prokineticin-2 (PROK2), respectively. The mutations in PROK2 were detected in the heterozygous state, whereas PROKR2 mutations were found in the heterozygous, homozygous, or compound heterozygous state. In addition, one of the patients heterozygous for a PROKR2 mutation was also carrying a missense mutation in KAL1, thus indicating a possible digenic inheritance of the disease in this individual. These findings reveal that insufficient prokineticin-signaling through PROKR2 leads to abnormal development of the olfactory system and reproductive axis in man. They also shed new light on the complex genetic transmission of Kallmann syndrome.
Kallmann syndrome is a developmental disease that affects both the hormonal reproductive axis and the sense of smell. In addition, various nonreproductive and nonolfactory anomalies are occasionally observed in a fraction of the patients. There is a developmental link between the reproductive and olfactory disorders: neuroendocrine cells producing the gonadotropin-releasing hormone that is deficient in the patients normally migrate from the nose to the forebrain along olfactory nerve fibers during embryonic life, and they most probably fail to do so in the patients. Affected individuals usually do not undergo spontaneous puberty. Hormone replacement therapy is the treatment to initiate virilization in males or breast development in females, and later, to develop fertility in both sexes. This is a hereditary disease with complex genetic transmission. Mutations in either of two different genes, KAL1 and FGFR1, have been found in approximately 20% of the affected individuals. The authors report on the identification (in a further 10% of patients) of various mutations in the prokineticin receptor-2 or prokineticin-2 genes, encoding a cell surface receptor and one of its ligands, respectively. Notably, some of the mutations were also detected in clinically unaffected individuals. This clearly indicates that additional, still unknown genetic or non-genetic factors are involved in disease production.
The Ran-binding protein 2 (RanBP2) is a large multimodular and pleiotropic protein. Several molecular partners with distinct functions interacting specifically with selective modules of RanBP2 have been identified. Yet, the significance of these interactions with RanBP2 and the genetic and physiological role(s) of RanBP2 in a whole-animal model remain elusive. Here, we report the identification of two novel partners of RanBP2 and a novel physiological role of RanBP2 in a mouse model. RanBP2 associates in vitro and in vivo and colocalizes with the mitochondrial metallochaperone, Cox11, and the pacemaker of glycolysis, hexokinase type I (HKI) via its leucine-rich domain. The leucine-rich domain of RanBP2 also exhibits strong chaperone activity toward intermediate and mature folding species of Cox11 supporting a chaperone role of RanBP2 in the cytosol during Cox11 biogenesis. Cox11 partially colocalizes with HKI, thus supporting additional and distinct roles in cell function. Cox11 is a strong inhibitor of HKI, and RanBP2 suppresses the inhibitory activity of Cox11 over HKI. To probe the physiological role of RanBP2 and its role in HKI function, a mouse model harboring a genetically disrupted RanBP2 locus was generated. RanBP2−/− are embryonically lethal, and haploinsufficiency of RanBP2 in an inbred strain causes a pronounced decrease of HKI and ATP levels selectively in the central nervous system. Inbred RanBP2+/− mice also exhibit deficits in growth rates and glucose catabolism without impairment of glucose uptake and gluconeogenesis. These phenotypes are accompanied by a decrease in the electrophysiological responses of photosensory and postreceptoral neurons. Hence, RanBP2 and its partners emerge as critical modulators of neuronal HKI, glucose catabolism, energy homeostasis, and targets for metabolic, aging disorders and allied neuropathies.
The Ran-binding protein 2 (RanBP2) is a large protein with several domains. Although several protein partners were found to interact with selective domains of RanBP2, none to this date were found toward its large leucine-rich domain (LD). Cell-based experiments support several roles of RanBP2 in cell function, such as the production of functional proteins, control of protein trafficking between the nuclear and cytosol compartments, and control of multiple facets underlying cell division. Still, the genetic and physiological implications of the interactions between RanBP2 and its partners and of the function of RanBP2 in a whole-animal model remain elusive. The authors report the identification of two novel mitochondrial partners of the LD of RanBP2, Cox11 and hexokinase type I (HKI); and with multidisciplinary approaches probe the role of RanBP2 and its LD on Cox11, HKI, and functions allied to these. The authors found that RanBP2 exhibits chaperone activity toward HKI and Cox11. RanBP2 and Cox11 profoundly modulate HKI activity. Moreover, partial loss-of-function of RanBP2 in a mouse model induces deficits in growth rates and breakdown of glucose, promotes the down-regulation of HKI and ATP levels selectively in the central nervous system, and impairs visual function. These findings support a critical role of RanBP2 and its partners in metabolic processes and allied disease states.
Delta-9 desaturases, also known as stearoyl-CoA desaturases, are lipogenic enzymes responsible for the generation of vital components of membranes and energy storage molecules. We have identified a novel nuclear hormone receptor, NHR-80, that regulates delta-9 desaturase gene expression in Caenorhabditis elegans. Here we describe fatty acid compositions, lifespans, and gene expression studies of strains carrying mutations in nhr-80 and in the three genes encoding delta-9 desaturases, fat-5, fat-6, and fat-7. The delta-9 desaturase single mutants display only subtle changes in fatty acid composition and no other visible phenotypes, yet the fat-5;fat-6;fat-7 triple mutant is lethal, revealing that endogenous production of monounsaturated fatty acids is essential for survival. In the absence of FAT-6 or FAT-7, the expression of the remaining desaturases increases, and this ability to compensate depends on NHR-80. We conclude that, like mammals, C. elegans requires adequate synthesis of unsaturated fatty acids and maintains complex regulation of the delta-9 desaturases to achieve optimal fatty acid composition.
The ratio of saturated to unsaturated fatty acids has a profound affect on the fluidity and function of cellular membranes. Animals, plants, and microorganisms regulate the synthesis of unsaturated fatty acids during changing environmental conditions, as well as in response to dietary nutrients. In this paper the authors use a combination of genetic and biochemical approaches to address the regulation of unsaturated fatty acid synthesis in the roundworm Caenorhabditis elegans. They identify a new transcription factor, NHR-80, that activates the expression of genes encoding delta-9 fatty acid desaturases, the enzymes responsible for catalyzing the insertion of double bonds into saturated fatty acid chains. These unsaturated fatty acids are critical components of membranes, as well as fat storage molecules. Experiments presented here demonstrate that the worms require adequate synthesis of unsaturated fatty acids for survival and that they maintain intricate regulation of the three delta-9 desaturase genes in response to different nutrients. Abnormalities in lipid metabolism lead to obesity and diabetes in humans; this study contributes to our understanding of the regulation of this metabolic pathway.
Cartilage-hair hypoplasia (CHH) is a pleiotropic disease caused by recessive mutations in the RMRP gene that result in a wide spectrum of manifestations including short stature, sparse hair, metaphyseal dysplasia, anemia, immune deficiency, and increased incidence of cancer. Molecular diagnosis of CHH has implications for management, prognosis, follow-up, and genetic counseling of affected patients and their families. We report 20 novel mutations in 36 patients with CHH and describe the associated phenotypic spectrum. Given the high mutational heterogeneity (62 mutations reported to date), the high frequency of variations in the region (eight single nucleotide polymorphisms in and around RMRP), and the fact that RMRP is not translated into protein, prediction of mutation pathogenicity is difficult. We addressed this issue by a comparative genomic approach and aligned the genomic sequences of RMRP gene in the entire class of mammals. We found that putative pathogenic mutations are located in highly conserved nucleotides, whereas polymorphisms are located in non-conserved positions. We conclude that the abundance of variations in this small gene is remarkable and at odds with its high conservation through species; it is unclear whether these variations are caused by a high local mutation rate, a failure of repair mechanisms, or a relaxed selective pressure. The marked diversity of mutations in RMRP and the low homozygosity rate in our patient population indicate that CHH is more common than previously estimated, but may go unrecognized because of its variable clinical presentation. Thus, RMRP molecular testing may be indicated in individuals with isolated metaphyseal dysplasia, anemia, or immune dysregulation.
Cartilage-hair hypoplasia is a genetic condition named after two of its most conspicuous features, short bones and sparse hair, but it affects blood-forming tissues, immune system, and intestine. It is caused by sequence mutations in RMRP, a small gene that codes for a structural RNA component of an RNAse complex whose biological functions have been elusive so far. The small RMRP gene carries a surprisingly high number of sequence variations, and because its transcript is not translated into protein and its function in the cell is still unclear, distinction between harmless variants and disease-causing mutations (more than 60 have been found so far by the authors and others) is difficult. The authors have sequenced the RMRP gene in several species covering the whole class of mammals and found that the gene is remarkably conserved between species. Interestingly, mutations occurring in conserved (probably functionally important) regions of the gene appear to be disease-producing, whereas those occurring in regions where evolution is more relaxed seem to be harmless variants. These results will help in counseling affected individuals and their families, and may lead to the discovery of the real function of this mysterious gene.
Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inherited disorder of mitochondrial fatty acid β-oxidation in humans. To better understand the pathogenesis of this disease, we developed a mouse model for MCAD deficiency (MCAD−/−) by gene targeting in embryonic stem (ES) cells. The MCAD−/− mice developed an organic aciduria and fatty liver, and showed profound cold intolerance at 4 °C with prior fasting. The sporadic cardiac lesions seen in MCAD−/− mice have not been reported in human MCAD patients. There was significant neonatal mortality of MCAD−/− pups demonstrating similarities to patterns of clinical episodes and mortality in MCAD-deficient patients. The MCAD-deficient mouse reproduced important aspects of human MCAD deficiency and is a valuable model for further analysis of the roles of fatty acid oxidation and pathogenesis of human diseases involving fatty acid oxidation.
Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is one of the most common inherited disorders of metabolism. This defect in fatty acid oxidation can lead to severe and sometimes fatal disease, especially in young children because they are unable to tolerate a fasting episode. Metabolic complications include very low blood glucose concentrations and generation of toxic by-products. This disorder can result in sudden infant death. Using a process known as gene targeting in mouse embryonic stem cells, the authors have developed a mouse model with the same enzyme deficiency. This mouse model of MCAD deficiency develops many of the same disease characteristics found in affected children. The MCAD-deficient mouse model shows a high rate of newborn loss, intolerance to cold, and the characteristic biochemical changes in the blood, tissues, and urine that are very similar to those found in the human disease counterpart. The MCAD-deficient mouse model will allow researchers to better understand disease mechanisms so that new preventive measures or therapies can be developed.
In glaucoma, harmful intraocular pressure often contributes to retinal ganglion cell death. It is not clear, however, if intraocular pressure directly insults the retinal ganglion cell axon, the soma, or both. The pathways that mediate pressure-induced retinal ganglion cell death are poorly defined, and no molecules are known to be required. DBA/2J mice deficient in the proapoptotic molecule BCL2-associated X protein (BAX) were used to investigate the roles of BAX-mediated cell death pathways in glaucoma. Both Bax+/− and Bax−/− mice were protected from retinal ganglion cell death. In contrast, axonal degeneration was not prevented in either Bax+/− or Bax−/− mice. While BAX deficiency did not prevent axonal degeneration, it did slow axonal loss. Additionally, we compared the effects of BAX deficiency on the glaucoma to its effects on retinal ganglion cell death due to two insults that are proposed to participate in glaucoma. As in the glaucoma, BAX deficiency protected retinal ganglion cells after axon injury by optic nerve crush. However, it did not protect retinal ganglion cells from N-methyl-D-aspartate (NMDA)-induced excitotoxicity. BAX is required for retinal ganglion cell death in an inherited glaucoma; however, it is not required for retinal ganglion cell axon degeneration. This indicates that distinct somal and axonal degeneration pathways are active in this glaucoma. Finally, our data support a role for optic nerve injury but not for NMDA receptor-mediated excitotoxicity in this glaucoma. These findings indicate a need to understand axon-specific degeneration pathways in glaucoma, and they suggest that distinct somal and axonal degeneration pathways may need to be targeted to save vision.
Glaucoma is a group of diseases whose unifying characteristic is death of nerve cells (retinal ganglion cells) that connect the eye to the brain. Glaucoma is often associated with a harmfully high pressure inside the eye (intraocular pressure) contributing to nerve cell death. Various treatments are used to lower eye pressure, but currently no commonly used treatments directly protect the nerve cells. DBA/2J mice develop elevated eye pressure with age, and this pressure kills retinal nerve cells. The authors use this mouse model to investigate how these nerve cells die in glaucoma. They show that there are distinct degeneration pathways activated in different parts of the retinal nerve cells. They found that the biochemical pathway in the nerve cell body, which resides in the retina, requires a molecule called BAX (BCL2-associated X protein). In contrast, pathways in the part of the cell (axon) that connects the cell body to the brain do not require BAX. Because degeneration pathways in the cell body and of the axon also may be molecularly different in human glaucoma, it will be important to consider them all when designing therapies. Their data also suggest that the BAX gene is a candidate to modulate glaucoma susceptibility.
Previously, we identified PHR1 as an abundantly expressed gene in photoreceptors and showed that it encodes four isoforms, each with N-terminal pleckstrin homology (PH) and C-terminal transmembrane domains. To better understand PHR1 function and expression, we made a Phr1 null mouse by inserting a β-galactosidase/neor cassette into exon 3. In addition to photoreceptors, we found abundant expression of specific Phr1 splice forms in olfactory receptor neurons and vestibular and cochlear hair cells. We also found Phr1 expression in cells with a possible sensory function, including peripheral retinal ganglion cells, cochlear interdental cells, and neurons of the circumventricular organ. Despite this discrete expression in known and putative sensory neurons, mice lacking PHR1 do not have overt sensory deficits.
The PEX11 peroxisomal membrane proteins promote peroxisome division in multiple eukaryotes. As part of our effort to understand the molecular and physiological functions of PEX11 proteins, we disrupted the mouse PEX11α gene. Overexpression of PEX11α is sufficient to promote peroxisome division, and a class of chemicals known as peroxisome proliferating agents (PPAs) induce the expression of PEX11α and promote peroxisome division. These observations led to the hypothesis that PPAs induce peroxisome abundance by enhancing PEX11α expression. The phenotypes of PEX11α−/− mice indicate that this hypothesis remains valid for a novel class of PPAs that act independently of peroxisome proliferator-activated receptor alpha (PPARα) but is not valid for the classical PPAs that act as activators of PPARα. Furthermore, we find that PEX11α−/− mice have normal peroxisome abundance and that cells lacking both PEX11α and PEX11β, a second mammalian PEX11 gene, have no greater defect in peroxisome abundance than do cells lacking only PEX11β. Finally, we report the identification of a third mammalian PEX11 gene, PEX11γ, and show that it too encodes a peroxisomal protein.
Zellweger syndrome is a lethal neurological disorder characterized by severe defects in peroxisomal protein import. The resulting defects in peroxisome metabolism and the accumulation of peroxisomal substrates are thought to cause the other Zellweger syndrome phenotypes, including neuronal migration defects, hypotonia, a developmental delay, and neonatal lethality. These phenotypes are also manifested in mouse models of Zellweger syndrome generated by disruption of the PEX5 or PEX2 gene. Here we show that mice lacking peroxisomal membrane protein PEX11β display several pathologic features shared by these mouse models of Zellweger syndrome, including neuronal migration defects, enhanced neuronal apoptosis, a developmental delay, hypotonia, and neonatal lethality. However, PEX11β deficiency differs significantly from Zellweger syndrome and Zellweger syndrome mice in that it is not characterized by a detectable defect in peroxisomal protein import and displays only mild defects in peroxisomal fatty acid β-oxidation and peroxisomal ether lipid biosynthesis. These results demonstrate that the neurological pathologic features of Zellweger syndrome can occur without peroxisomal enzyme mislocalization and challenge current models of Zellweger syndrome pathogenesis.